1. Field of the Invention
The present invention relates to a particulate matter detection device and an inspection method of the particulate matter detection device. More particularly, it relates to a particulate matter detection device which can judge whether or not detection of a particulate matter by the particulate matter detection device is normally performed and satisfactorily inspect the device for break-down or defect of the device, and an inspection method of the particulate matter detection device.
2. Description of the Related Art
A flue exhaust gas or a diesel engine exhaust gas contains a particulate matter (PM) such as soot, which has been a cause for air pollution. To remove the particulate matter, a filter (a diesel particulate filter: DPF) made of a ceramic material or the like has broadly been used. The ceramic DPF can be used for a long period of time, but defects such as cracks and melting damages occur owing to thermal deterioration or the like sometimes, and a micro amount of particulate matter might leak. In case of the occurrence of such a defect, it is remarkably important from the viewpoint of prevention of the air pollution to readily detect the occurrence of the defect and recognize an abnormality of a device.
Examples of a method of detecting the occurrence of such a defect include a method of disposing a particulate matter detection device on the downstream side of the DPF (e.g., see Patent Document 1).
In the invention disclosed in Patent Document 1, a particulate matter is charged by corona discharge to measure an ion current, thereby measuring the amount of the particulate matter. In this way, in the method of charging the particulate matter to measure the ion current thereof, the ion current which charges the particulate matter is weak, and hence a large-scale detection circuit is necessary for detecting the weak ion current, whereby the method becomes expensive. Moreover, when an exhaust gas has a high flow rate, it is difficult to effectively charge the particulate matter. Therefore, the measured value of the particulate matter becomes smaller than a value of the amount of the particulate matter actually contained in the exhaust gas, so that an error of the value increases.
To solve such a problem, for example, there has been suggested a particulate matter detection device or the like comprising a unidirectionally long detection device main body having one end portion provided with one through hole, and at least a pair of electrodes embedded in a wall of the through hole and covered with a dielectric material. A particulate matter in an exhaust gas can electrically be adsorbed by the wall face of the through hole, and a change of electrical characteristics of the wall of the through hole can be measured to detect a mass of the particulate matter adsorbed by the wall face of the through hole (see Patent Document 2).
Moreover, there has been suggested an inspection method or system for confirming a normal operation of a detection device which measures a size of an ion current to measure a particulate matter in an exhaust gas as disclosed in Patent Document 1 (e.g., see Patent Document 3).
[Patent Document 1] JP-A-60-123761
[Patent Document 2] JP-A-2009-186278
[Patent Document 3] JP-A-2006-503270